In high-pressure water blasting operations, it is often desirable to rotate a nozzle head to increase surface coverage, and thus productivity. However, sealing between the stationary and rotating components of the water blasting system must be addressed. The high-pressure environment and relative motion between components accelerate wear on the sealing components. For this reason, the sealing components must be changed regularly. The length of time required for this maintenance reduces the productivity of the water blasting system. Multiple solutions have been developed to address this sealing problem.
In one solution, in which seal members are not used, the stationary and rotating components are separated by a very small space, for example less than a thousandth of an inch. The working fluid is allowed to escape through this space. Since there is no contact between the components, friction is minimized. In this solution, the power used to pressurize the fluid which escapes is wasted as it does not flow through the nozzle. At ultra-high pressures, near 40,000 PSI, this can be as much as 30% of the power used in the system.
In another solution, sealing is accomplished using a plastic seal member bearing against a metal mandrel. The pressure of the working fluid forces the plastic seal member against the mandrel, preventing the working fluid from escaping. The plastic seal member is typically supported by a metal backup bushing. While this seal design is quite popular, the maintenance of this design is complicated and time consuming. This seal design uses a number of small parts which are removed and replaced separately. Removing and installing these small parts increases the time required to service the assembly, decreasing overall water blasting system productivity. Further, as such parts are often changed in the field, there is an inherent risk that some of the parts may be mishandled and either damaged or lost. Improvements are desired.